Solar Panel Sizing
How to Size Your Solar Panels
Step-by-step guide to calculating the right number of panels for your home.
8 min read
Simple and practical
Beginner level
No solar background needed
PH context
Made for local homes
What you will understand
Visual Learning Map
Lesson Guide
Panel Sizing Formula
Step 1: Find daily consumption
Daily kWh = Monthly Bill (₱) ÷ Grid Rate (₱/kWh) ÷ 30
Step 2: Account for sun hours
Required kW = Daily kWh ÷ Peak Sun Hours ÷ 0.80 (efficiency)
Step 3: Calculate panels
Panel Count = (Required kW × 1000) ÷ Panel Wattage
Worked Example
- Monthly bill: ₱6,000
- Grid rate: ₱12/kWh
- Daily kWh: 6000 ÷ 12 ÷ 30 = 16.7 kWh/day
- Peak sun hours (Manila): 4.5 hrs
- Required kW: 16.7 ÷ 4.5 ÷ 0.8 = 4.6 kW
- Panels (550W): 4600 ÷ 550 = 9 panels
Use our System Sizing Calculator for instant results!
Frequently Asked Questions
Should I size for 100% of my bill?
Aim for 70–90% for best ROI. Oversizing hits diminishing returns without net metering export value.
What are peak sun hours?
Equivalent hours of full-intensity sun per day. PH average: 4.0–5.5 depending on region.
Does panel angle matter?
Yes. 10–15° tilt facing south is optimal for most PH locations.
What is system efficiency?
Accounts for inverter losses, wiring, dust, and heat. Use 0.75–0.85 (we use 0.80).
Can I add panels later?
Yes, if your inverter and roof have capacity. Plan 20% headroom on inverter size.
Common Mistakes to Avoid
Using nameplate wattage only
Panels rarely hit rated wattage in real conditions. Use 80% system efficiency factor.
Not accounting for future loads
Adding EV, new aircon, or appliances? Size 10–20% larger now.
Ignoring roof space limits
Measure available roof area. Each 550W panel needs ~2.5 m².